Blood glucose level measurement device and blood glucose level measurement method

Abstract

This blood glucose level measurement device comprises: a light output unit that outputs light; a light detection unit that detects light that has been output by the light output unit and passed through a living body; a temporal phase difference calculation unit that, on the basis of the detection result of the light detection unit, calculates the temporal phase difference between an oxygenated hemoglobin waveform pertaining to the oxygenated hemoglobin concentration of the blood of the living body and a deoxygenated hemoglobin waveform pertaining to the deoxygenated hemoglobin concentration of the blood of the living body; a blood glucose level calculation unit that calculates the blood glucose level of the living body on the basis of the calculated temporal phase difference; a level of similarity estimation unit that estimates the level of waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform; and a reliability estimation unit that estimates the reliability of the calculated blood glucose level. The reliability estimation unit estimates that the reliability becomes smaller as the level of waveform similarity becomes smaller.

Description

Blood glucose level measuring device and blood glucose level measuring method

[0001] The present disclosure relates to a blood glucose level measuring device and a blood glucose level measuring method.

[0002] Known technology for measuring blood glucose levels in a living organism is, for example, the device described in Patent Document 1. The device described in Patent Document 1 calculates a temporal phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration in the blood of the living organism based on the detection result of light transmitted through the living organism, and calculates the blood glucose level of the living organism based on the temporal phase difference.

[0003] JP 2018-57511 A

[0004] The above-described techniques enable non-invasive and accurate measurement of blood glucose levels in living organisms. However, there are cases where such techniques require further improvement in the accuracy of blood glucose level measurement.

[0005] An object of the present disclosure is to provide a blood glucose level measuring device and a blood glucose level measuring method that are capable of measuring the blood glucose level of a living body with high accuracy.

[0006] The blood glucose level measuring device of the present disclosure is [1] "a blood glucose level measuring device that measures a blood glucose level of a living organism, comprising: a light output unit that outputs light to the living organism; a light detection unit that detects the light output by the light output unit and transmitted through the living organism; a temporal phase difference calculation unit that calculates a temporal phase difference between an oxygenated hemoglobin waveform related to an oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform related to a deoxygenated hemoglobin concentration in the blood of the living organism based on a detection result of the light detection unit; a blood glucose level calculation unit that calculates the blood glucose level of the living organism based on the temporal phase difference calculated by the temporal phase difference calculation unit; a similarity estimation unit that estimates a waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform; and a reliability estimation unit that estimates a reliability of the blood glucose level calculated by the blood glucose level calculation unit, wherein the reliability estimation unit estimates that the reliability decreases as the waveform similarity decreases."

[0007] In the blood glucose level measuring device described in [1] above, the blood glucose level calculation unit calculates the blood glucose level of the living body based on the temporal phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration in the blood of the living body and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration in the blood of the living body. This allows the blood glucose level of the living body to be measured appropriately. Furthermore, the similarity estimation unit estimates the waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform, and the reliability estimation unit estimates that the smaller the waveform similarity, the lower the reliability of the blood glucose level calculated by the blood glucose level calculation unit. This makes it possible to calculate a blood glucose level with estimated reliability. Therefore, this blood glucose level measuring device allows the blood glucose level of the living body to be measured accurately.

[0008] The blood glucose measuring device of the present disclosure may be [2] "the blood glucose measuring device according to the above [1], wherein the similarity estimating unit estimates the waveform similarity based on a normalized oxygenated hemoglobin waveform obtained by dividing the oxygenated hemoglobin waveform by the peak value of the oxygenated hemoglobin waveform and a normalized deoxygenated hemoglobin waveform obtained by dividing the deoxygenated hemoglobin waveform by the peak value of the deoxygenated hemoglobin waveform." This allows the waveform similarity to be estimated with high accuracy.

[0009] The blood glucose measuring device of the present disclosure may be [3] "the blood glucose measuring device according to the above [2], wherein the similarity estimating unit estimates that the waveform similarity is smaller as the standard deviation calculated based on the following formula (1) is larger." This allows the waveform similarity to be estimated with high accuracy.

[0010] where σ is the standard deviation, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

[0011] The blood glucose measuring device of the present disclosure may be [4] "the blood glucose measuring device according to the above [3], wherein the similarity estimating unit estimates that the waveform similarity is greater as the first relative quality index calculated based on the following formulas (2) and (3) is closer to 1." This allows the waveform similarity to be estimated with high accuracy.

[0012] where R1 is the first relative quality index, σ is the standard deviation, σt is the theoretical limit value of the standard deviation, and Δθ is the temporal phase difference.

[0013] The blood glucose measuring device of the present disclosure may be [5] "the blood glucose measuring device according to the above [2], wherein the similarity estimating unit estimates that the waveform similarity is greater as the standard inner product calculated based on the following formula (4) is closer to 1." This allows the waveform similarity to be estimated with high accuracy.

[0014] where P is the standard inner product, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

[0015] The blood glucose measuring device of the present disclosure may be [6] "the blood glucose measuring device according to the above [2], wherein the similarity estimating unit estimates that the waveform similarity is smaller as the absolute mean error calculated based on the following formula (5) is larger." This allows the waveform similarity to be estimated with high accuracy.

[0016] where M is the absolute mean error, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

[0017] The blood glucose measuring device of the present disclosure may be [7] "the blood glucose measuring device according to the above [6], wherein the similarity estimating unit estimates that the waveform similarity is greater as the second relative quality index calculated based on the following formulas (6) and (7) is closer to 1." This allows the waveform similarity to be estimated with high accuracy.

[0018] where R2 is the second relative quality index, M is the absolute mean error, Mt is the theoretical limit value of the absolute mean error, and Δθ is the temporal phase difference.

[0019] The blood glucose measuring device of the present disclosure may be [8] "the blood glucose measuring device according to the above [2], wherein the similarity estimating unit estimates the waveform similarity based on image recognition results of the oxygenated hemoglobin normalized waveform and the deoxygenated hemoglobin normalized waveform." This allows for accurate estimation of waveform similarity.

[0020] The blood glucose measuring device of the present disclosure may be [9] "the blood glucose measuring device according to any one of [2] to [8] above, wherein the similarity estimating unit estimates the waveform similarity based on a region from a bottom point to a peak point of the normalized oxygenated hemoglobin waveform and a region from a bottom point to a peak point of the normalized deoxygenated hemoglobin waveform." This allows for efficient estimation of waveform similarity.

[0021] The blood glucose measuring device of the present disclosure may be

[10] "the blood glucose measuring device according to any one of the above [1] to [9], further comprising a notification unit that issues a remeasurement notification when the waveform similarity is smaller than a predetermined threshold value." This makes it possible to prompt the person measuring the blood glucose level to remeasure.

[0022] The blood glucose level measuring device of the present disclosure may be the blood glucose level measuring device according to any one of [1] to

[10] above,

[11] , wherein "the light detecting unit detects, as the light transmitted through the living body, first light having a first wavelength, second light having a second wavelength, and third light having a third wavelength; and the temporal phase difference calculating unit calculates the temporal phase difference based on the detection results of either the first light or the second light and the third light when the waveform similarity calculated based on the detection results of the first light and the second light is smaller than a predetermined threshold value; and the third wavelength is greater than the first wavelength and less than the second wavelength." This ensures both the accuracy of spectroscopic measurement and the waveform similarity, enabling accurate measurement of blood glucose levels.

[0023] The blood glucose level measurement method of the present disclosure is

[12] "a blood glucose level measurement method for measuring a blood glucose level of a living organism, comprising: a temporal phase difference calculation step of calculating a temporal phase difference between an oxygenated hemoglobin waveform relating to an oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform relating to a deoxygenated hemoglobin concentration in the blood of the living organism based on a detection result of light transmitted through the living organism; a blood glucose level calculation step of calculating the blood glucose level of the living organism based on the temporal phase difference calculated in the temporal phase difference calculation step; a similarity estimation step of estimating a waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform; and a reliability estimation step of estimating a reliability of the blood glucose level calculated in the blood glucose level calculation step, wherein in the reliability estimation step, it is estimated that the reliability is lower as the waveform similarity is lower."

[0024] According to the blood glucose level measuring method described in

[12] above, it is possible to measure the blood glucose level of a living body with high accuracy, similar to the blood glucose level measuring device described above.

[0025] The blood glucose level measurement method of the present disclosure may be

[13] "the blood glucose level measurement method according to the above

[12] , further comprising a light output step of outputting the light to the living body, and a light detection step of detecting the light output in the light output step and transmitted through the living body." This makes it possible to accurately measure the blood glucose level of a living body, similar to the blood glucose level measurement device described above.

[0026] According to the present disclosure, it is possible to provide a blood glucose level measuring device and a blood glucose level measuring method that are capable of measuring the blood glucose level of a living body with high accuracy.

[0027] 1 is a conceptual diagram of a blood glucose level measuring device according to an embodiment; FIG. 2 is a detection result of a light detection unit shown in FIG. 1; FIG. 3 is a block diagram showing the functional configuration of an ECU shown in FIG. 2; FIG. 4 is a schematic diagram of the oxygenated hemoglobin waveform and deoxygenated hemoglobin waveform shown in FIG. 5; FIG. 6 is a schematic diagram of a normalized oxygenated hemoglobin waveform and a normalized deoxygenated hemoglobin waveform; FIG. 7 is a schematic diagram of a normalized oxygenated hemoglobin waveform and a normalized deoxygenated hemoglobin waveform; FIG. 8 is a diagram showing an optical path of measurement light of each wavelength; FIG. 9 is a diagram showing an example of a method for estimating the waveform similarity between an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform; FIG. 10 is a diagram showing an example of a method for estimating the waveform similarity between an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform; FIG. 11 is a diagram showing a threshold value for the waveform similarity between an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform; Fig. 1 is a flowchart showing each step of a blood glucose level measurement method according to one embodiment. Fig. 2 is a flowchart showing each step of a blood glucose level measurement method according to one embodiment. Fig. 3 is a diagram showing a method for estimating the waveform similarity between an oxygenated hemoglobin waveform and a deoxygenated hemoglobin waveform according to a modified example.

[0028] Hereinafter, the embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0029] Fig. 1 is a cross-sectional view of a blood glucose level measuring device and a living body according to this embodiment. Fig. 1 is merely a conceptual diagram for explaining the function of the blood glucose level measuring device 1, and does not necessarily show an actual cross-section of the blood glucose level measuring device 1.

[0030] The blood glucose level measuring device 1 shown in Fig. 1 is, for example, a wearable device, a smartphone, or a pulse oximeter. Examples of wearable devices include a smart watch and a smart ring. In this embodiment, the blood glucose level measuring device 1 is a smart watch that has a function of measuring the blood glucose level of a living body 6. The living body 6 has a superficial tissue 61 and an internal tissue 62 that is located more internally than the superficial tissue 61. The surface 61a of the superficial tissue 61 is the surface of the skin of the living body 6. The living body 6 is, for example, a human body.

[0031] The blood glucose measuring device 1 measures the blood glucose level of a living organism 6. The blood glucose measuring device 1 includes a main body 2, a light output unit 3, a light detection unit 4, and an ECU (Electronic Control Unit) 5. The main body 2 has a front face 2a and a back face 2b facing the opposite side to the front face 2a. The front face 2a functions as a display screen that displays various information about the blood glucose measuring device 1. The blood glucose measuring device 1 is attached to the living organism 6 so that the back face 2b comes into contact with the skin of the living organism 6.

[0032] The light output unit 3 is provided in the main body 2. The light output surface of the light output unit 3 is exposed from the back surface 2b of the main body 2. The light output unit 3 has a light source that outputs measurement light L to the living body 6. The light source is, for example, a light-emitting diode (LED), a laser diode (LD), or a superluminescent diode (SLD). The measurement light L is emitted from the back surface 2b. The measurement light L emitted from the light output unit 3 propagates inside the living body 6 and is then emitted again from the living body 6. The light output unit 3 is controlled by the ECU 5.

[0033] The wavelength range of the measurement light L is, for example, from the red wavelength region of visible light to the near-infrared region (670 nm to 2500 nm). That is, the light output unit 3 outputs measurement light L included in the range from the red wavelength region of visible light to the near-infrared region. The light output unit 3 outputs measurement light L, for example, having wavelengths different from each other. The light output unit 3 has multiple light sources. In this embodiment, the light output unit 3 has a first light source, a second light source, and a third light source. The first light source outputs first measurement light L1 having a first wavelength (see FIG. 8), the second light source outputs second measurement light L2 having a second wavelength (see FIG. 8), and the third light source outputs third measurement light L3 having a third wavelength (see FIG. 8).

[0034] The second wavelength of the second measurement light L2 is longer than the first wavelength of the first measurement light L1. The third wavelength of the third measurement light L3 is longer than the first wavelength and shorter than the second wavelength. In this embodiment, the first wavelength is, for example, about 735 nm, the second wavelength is, for example, about 850 nm, and the third wavelength is, for example, about 810 nm. Note that the light output unit 3 may have a single light source that outputs probe light (e.g., white light) containing different wavelength components (the above-mentioned first wavelength, second wavelength, and third wavelength).

[0035] The light detection unit 4 is provided in the main body 2. The light detection unit 4 is separated from the light output unit 3. The light detection surface of the light detection unit 4 is exposed from the rear surface 2b of the main body 2. The light detection unit 4 has a light detection element that detects the measurement light (transmitted light) L output from the light output unit 3 and transmitted through the living body 6. The light detection element is, for example, a photodiode (PD). The light detection unit 4 also has a preamplifier that amplifies the photocurrent output from the light detection element and an A / D conversion circuit that converts the signal amplified by the preamplifier into a digital signal. The light detection unit 4 may have a CCD image sensor or a CMOS image sensor. The light detection unit 4 detects the first measurement light L1, the second measurement light L2, and the third measurement light L3 that have transmitted through the living body 6. The light detection unit 4 transmits a signal related to the intensity of the measurement light L to the ECU 5.

[0036] 2, the light detection unit 4 detects at least first data D1 and second data D2. The first data D1 is, for example, a change over time in the intensity of a first measurement light (transmitted light) L1 that has passed through the living body 6 and entered the light detection unit 4, and the second data D2 is, for example, a change over time in the intensity of a second measurement light (transmitted light) L2 that has passed through the living body 6 and entered the light detection unit 4. Each of the first data D1 and the second data D2 periodically fluctuates over time. Note that the respective periods of the first data D1 and the second data D2 approximately coincide with the cardiac cycle of the living body 6.

[0037] The ECU 5 is provided in the main body 2. The ECU 5 is an electronic control unit having a central processing unit (CPU) and a storage unit such as a read-only memory (ROM) or a random access memory (RAM). In the ECU 5, for example, a program stored in the storage unit is executed by the CPU. The ECU 5 calculates the blood glucose level, pulse rate, and oxygen saturation concentration of the living body 6 based on a signal (detection result of the light detection unit 4) transmitted from the light detection unit 4. FIG. 3 is a block diagram showing the functional configuration of the ECU 5. As shown in FIG. 3, the ECU 5 includes a temporal phase difference calculation unit 51, a blood glucose level calculation unit 52, a similarity estimation unit 53, a reliability estimation unit 54, and a notification unit 55.

[0038] 4, the temporal phase difference calculation unit 51 calculates an oxygenated hemoglobin waveform P1 and a deoxygenated hemoglobin waveform P2 based on the detection result of the light detection unit 4. The oxygenated hemoglobin waveform P1 is a waveform of oxygenated hemoglobin (O ２ The first data D1 and the second data D2 are data relating to the concentration of deoxygenated hemoglobin (HHb), and the deoxygenated hemoglobin waveform P2 is data relating to the concentration of deoxygenated hemoglobin (HHb) in the blood of the living body 6. The temporal phase difference calculation unit 51 calculates the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 by performing spectroscopic calculation processing based on, for example, the Modified Beer-Lambert (MBL) method on the first data D1 and the second data D2.

[0039] Specifically, the temporal phase difference calculation unit 51 calculates the difference between the intensity of the first data D1 at the first time and the intensity of the first data D1 at the second time (the amount of change over time in the intensity of the first data D1), the difference between the intensity of the second data D2 at the first time and the intensity of the second data D2 at the second time (the amount of change over time in the intensity of the second data D2), the absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin for the first data D1, and the O absorption coefficient for the second data D2. ２ Based on the respective absorption coefficients of Hb and HHb, the relative change in oxygenated hemoglobin over time (ΔO ２ The temporal phase difference calculation unit 51 calculates the temporal relative change in ΔO ２ Hb and ΔHHb are continuously calculated at predetermined time intervals (for example, about 16 milliseconds). ２ The change in Hb over time is the oxygenated hemoglobin waveform P1 shown in Fig. 4, and the change in ΔHHb over time is the deoxygenated hemoglobin waveform P2 shown in Fig. 4. The concentration index on the vertical axis in Fig. 4 is, for example, a volume concentration index (concentration x optical path length).

[0040] The temporal phase difference calculation unit 51 calculates the temporal phase difference (hereinafter simply referred to as "temporal phase difference") between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2. FIG. 5 is a schematic diagram of the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 shown in FIG. 4. The temporal phase difference calculation unit 51 calculates the time difference between a first characteristic point C1 of the oxygenated hemoglobin waveform P1 and a second characteristic point C2 of the deoxygenated hemoglobin waveform P2 as the temporal phase difference Δθ. In this embodiment, the first characteristic point C1 is a bottom point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 is a bottom point of the deoxygenated hemoglobin waveform P2. The first characteristic point C1 may be, for example, a peak point or a notch point of the oxygenated hemoglobin waveform P1, and the second characteristic point C2 may be, for example, a peak point or a notch point of the deoxygenated hemoglobin waveform P2. In this embodiment, the methods disclosed in Japanese Patent No. 6846152, for example, are used to calculate the temporal phase difference Δθ.

[0041] The blood glucose level calculation unit 52 calculates the blood glucose level of the living organism 6 based on the temporal phase difference Δθ calculated by the temporal phase difference calculation unit 51. The blood glucose level calculation unit 52 calculates the blood glucose level of the living organism 6 using the formula G = α × Δθ - β, where G is the blood glucose level of the living organism 6, Δθ is the temporal phase difference, and α and β are coefficients determined according to the glucose metabolic capacity and the measurement site of the living organism 6. In this embodiment, the methods disclosed in Japanese Patent No. 6846152, for example, are used as blood glucose level calculation methods.

[0042] Incidentally, the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 (hereinafter simply referred to as "waveform similarity") may affect the accuracy of blood glucose measurement. FIGS. 6 and 7 are schematic diagrams of an oxygenated hemoglobin normalized waveform and a deoxygenated hemoglobin normalized waveform, respectively. The oxygenated hemoglobin normalized waveform P11 shown in FIGS. 6 and 7 is a waveform obtained by dividing the oxygenated hemoglobin waveform P1 by the peak value of the oxygenated hemoglobin waveform P1. The peak value of the oxygenated hemoglobin normalized waveform P11 is 1. The deoxygenated hemoglobin normalized waveform P21 shown in FIGS. 6 and 7 is a waveform obtained by dividing the deoxygenated hemoglobin waveform P2 by the peak value of the deoxygenated hemoglobin waveform P2. The peak value of the deoxygenated hemoglobin normalized waveform P21 is 1.

[0043] As shown in Fig. 6, the greater the degree of coincidence between the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21, the greater the waveform similarity. As shown in Fig. 7, the smaller the degree of coincidence between the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21, the smaller the waveform similarity. Note that Figs. 6 and 7 each show only one cycle of the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21.

[0044] The present inventors have found that the greater the waveform similarity, the greater the blood glucose measurement accuracy tends to be, and the smaller the waveform similarity, the smaller the blood glucose measurement accuracy tends to be. The reason for this is as follows: FIG. 8 is a diagram showing the optical path of the measurement light output from the light output unit 3. As shown in FIG. 8, the first measurement light L1, the second measurement light L2, and the third measurement light L3 output from the light output unit 3 each travel different optical paths before entering the light detection unit 4. The longer the wavelength of the measurement light, the longer the optical path length within the living body 6 tends to be. Because the second wavelength of the second measurement light L2 is longer than the first wavelength of the first measurement light L1, the optical path length of the second measurement light L2 is longer than the optical path length of the first measurement light L1. Because the third wavelength of the third measurement light L3 is longer than the first wavelength of the first measurement light L1 and shorter than the second wavelength of the second measurement light L2, the optical path length of the third measurement light L3 is longer than the optical path length of the first measurement light L1 and shorter than the optical path length of the second measurement light L2.

[0045] For example, the greater the similarity between the tissue characteristics of the living body 6 in the first measurement light L1 and the tissue characteristics of the living body 6 in the optical path of the second measurement light L2, the greater the reliability of the blood glucose level calculated based on the detection results of the first measurement light L1 and the second measurement light L2. For example, the greater the similarity between the tissue characteristics of the living body 6 in the first measurement light L1 and the tissue characteristics of the living body 6 in the optical path of the second measurement light L2, the greater the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2. The tissue characteristics of the living body 6 include, for example, the type of tissue, the Young's modulus (elastic coefficient) of the tissue, or the tissue density. The present inventors attempted to estimate the reliability of the blood glucose level by estimating the similarity between the tissue characteristics of the living body 6 in the optical path of each measurement light based on the waveform similarity.

[0046] The similarity estimation unit 53 estimates the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2. As shown in Fig. 9 , the similarity estimation unit 53 estimates the waveform similarity based on the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21. The similarity estimation unit 53 estimates that the waveform similarity decreases as the standard deviation calculated based on the following formula (8) increases. In other words, the similarity estimation unit 53 estimates that the waveform similarity decreases as the reciprocal of the standard deviation (quality index) decreases.

[0047] σ: Standard deviation n: Number of samples (an integer of 2 or more) p ｋ q: Value of the oxygenated hemoglobin normalized waveform P11 at the kth time ｋ : Value of the deoxygenated hemoglobin normalized waveform P21 at the kth time

[0048] The similarity estimation unit 53 estimates the waveform similarity based on at least a partial region of one cycle of the oxygenated hemoglobin normalized waveform P11 and at least a partial region of one cycle of the deoxygenated hemoglobin normalized waveform P21. In the present embodiment, the similarity estimation unit 53 estimates the waveform similarity based on one cycle of the oxygenated hemoglobin normalized waveform P11 (e.g., the region between adjacent bottom points) and one cycle of the deoxygenated hemoglobin normalized waveform P21 (e.g., the region between adjacent bottom points).

[0049] When it is assumed that the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21 are each a sine wave, the theoretical limit value σt of the standard deviation σ is (1−cos Δθ) １／２ The similarity estimation unit 53 estimates that the waveform similarity is greater as the reciprocal of the standard deviation σ approaches the reciprocal of the theoretical limit value σt. That is, the similarity estimation unit 53 estimates that the waveform similarity is greater as the first relative quality index calculated based on the following equations (9) and (10) approaches 1.

[0050] R1: First relative quality index σ: Standard deviation σt: Theoretical limit of standard deviation Δθ: Temporal phase difference

[0051] Fig. 10 is a diagram showing the correlation between the reciprocal of the standard deviation σ and the temporal phase difference Δθ. Fig. 10 shows a theoretical correlation T between the reciprocal of the theoretical limit value σt and the temporal phase difference Δθ, and a plot of the reciprocal of the standard deviation σ and the temporal phase difference Δθ calculated based on the detection results of the light detection unit 4. The similarity estimation unit 53 estimates that the closer the position of the plot is to the theoretical correlation T, the greater the waveform similarity.

[0052] The similarity estimation unit 53 estimates whether the waveform similarity is smaller than a predetermined threshold. FIG. 11 is a diagram showing the upper and lower thresholds of the waveform similarity. As shown in FIG. 11, the upper threshold Tu is a line offset from the theoretical correlation T in the positive direction (the direction in which both Δθ and 1 / σ increase), and the lower threshold Tl is a line offset from the theoretical correlation T in the negative direction (the direction in which both Δθ and 1 / σ decrease). FIG. 12 is a graph in which the vertical axis of FIG. 11 is replaced with the first relative quality index R1. As shown in FIG. 12, in this embodiment, the upper threshold Tu is 1.2 times the theoretical correlation T, and the lower threshold Tl is 0.8 times the theoretical correlation T.

[0053] The similarity estimation unit 53 estimates that the waveform similarity is equal to or greater than the threshold value when a plot of the reciprocal of the standard deviation σ calculated based on the detection results of the light detection unit 4 and the temporal phase difference Δθ is located inside a region (sweet spot) defined by an upper threshold Tu and a lower threshold Tl. The similarity estimation unit 53 estimates that the waveform similarity is smaller than the threshold value when the plot is located outside the sweet spot. Note that the similarity estimation unit 53 estimates that the waveform similarity is equal to or greater than the threshold value when the plot overlaps with the upper threshold Tu or the lower threshold Tl.

[0054] If there is an error in the calculation result of the temporal phase difference Δθ by the temporal phase difference calculation unit 51, an error will also occur in the calculation result of the theoretical limit value σt, and as a result, the first relative quality index R1 may deviate from 1 (the position of the plot may deviate from the theoretical correlation T). For example, if the temporal phase difference Δθ calculated by the temporal phase difference calculation unit 51 is larger than the actual temporal phase difference, the theoretical limit value σt calculated based on the above equation (10) also tends to be larger, and as a result, the first relative quality index R1 calculated based on the above equation (9) tends to be larger than 1. As such, the calculation accuracy of the temporal phase difference Δθ is extremely important in estimating the waveform similarity. If the calculation accuracy of the temporal phase difference Δθ by the temporal phase difference calculation unit 51 is relatively low, the similarity estimation unit 53 estimates that the waveform similarity is also relatively low.

[0055] The reliability estimation unit 54 estimates the reliability of the blood glucose level calculated by the blood glucose level calculation unit 52. The reliability estimation unit 54 estimates that the greater the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 used to calculate the blood glucose level, the greater the reliability of the blood glucose level. If the waveform similarity is equal to or greater than the threshold, the reliability estimation unit 54 estimates that the blood glucose level is highly reliable. If the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 used to calculate the blood glucose level is smaller, the reliability estimation unit 54 estimates that the blood glucose level is less reliable. If the waveform similarity is smaller than the threshold, the reliability estimation unit 54 estimates that the blood glucose level is less reliable.

[0056] The notification unit 55 displays the reliability estimated by the reliability estimation unit 54 together with the blood glucose level calculated by the blood glucose level calculation unit 52 on the display screen of the main unit 2. If the waveform similarity is smaller than the threshold value, the notification unit 55 executes a remeasurement notification. The notification unit 55 sounds an alarm for remeasurement, for example, via a speaker provided in the main unit 2. The notification unit 55 may, for example, display a remeasurement icon on the display screen of the main unit 2. When a remeasurement notification is executed, the person measuring the blood glucose level remeasures the blood glucose level, for example, after adjusting the wearing position of the blood glucose measuring device 1.

[0057] The greater the wavelength difference between the two measurement lights used to calculate the temporal phase difference Δθ, the more accurate the spectroscopic calculation. However, as described above, the greater the wavelength difference between the measurement lights, the greater the difference in optical path length of the measurement lights, and therefore the higher the probability that the tissue characteristics of the living body 6 in each optical path of the two measurement lights will be different. The temporal phase difference calculation unit 51 prioritizes the accuracy of the spectroscopic calculation and first calculates the temporal phase difference Δθ based on the detection results of the first measurement light L1 and the second measurement light L2. If the waveform similarity calculated based on the detection results of the first measurement light L1 and the second measurement light L2 is smaller than the threshold, the temporal phase difference calculation unit 51 may calculate the temporal phase difference Δθ based on the detection results of the first measurement light L1 and the third measurement light L3. If the waveform similarity calculated based on the detection results of the first measurement light L1 and the second measurement light L2 is smaller than the threshold, the temporal phase difference calculation unit 51 may calculate the temporal phase difference Δθ based on the detection results of the second measurement light L2 and the third measurement light L3.

[0058] Next, the blood glucose level measurement method of this embodiment will be described. As shown in Fig. 13, in the blood glucose level measurement method of this embodiment, first, measurement light L is output to the living body 6 (step S1). Step S1 corresponds to a light output step. Next, the measurement light L output in step S1 and transmitted through the living body 6 is detected (step S2). Step S2 corresponds to a light detection step. Next, based on the detection result of the measurement light L transmitted through the living body 6, a temporal phase difference Δθ between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 is calculated (step S3). Step S3 corresponds to a temporal phase difference calculation step.

[0059] Next, the blood glucose level of the living body 6 is calculated based on the temporal phase difference Δθ calculated in step S3 (step S4). Step S4 corresponds to the blood glucose level calculation step. Next, the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2 is estimated (step S). Step S5 corresponds to the similarity estimation step. Next, the reliability of the blood glucose level calculated in step S4 is estimated (step S6). In step S6, it is estimated that the smaller the waveform similarity, the lower the reliability of the blood glucose level. Step S6 corresponds to the reliability estimation step.

[0060] 14, it is then determined whether the waveform similarity estimated in step S5 is equal to or greater than the threshold (step S7). If it is determined in step S7 that the waveform similarity is equal to or greater than the threshold (step S7: YES), the blood glucose level calculated in step S4 is notified (step S8). In step S8, the blood glucose level and the reliability of the blood glucose level are also notified. If it is determined in step S7 that the waveform similarity is less than the threshold (step S7: NO), a notification to remeasure is issued (step S9).

[0061] As described above, in the blood glucose level measuring device 1, the blood glucose level calculation unit 52 calculates the blood glucose level of the living body 6 based on the temporal phase difference Δθ between the oxygenated hemoglobin waveform P1 relating to the oxygenated hemoglobin concentration in the blood of the living body 6 and the deoxygenated hemoglobin waveform P2 relating to the deoxygenated hemoglobin concentration in the blood of the living body 6. This allows the blood glucose level of the living body 6 to be measured appropriately. Furthermore, the similarity estimation unit 53 estimates the waveform similarity between the oxygenated hemoglobin waveform P1 and the deoxygenated hemoglobin waveform P2, and the reliability estimation unit 54 estimates that the smaller the waveform similarity, the lower the reliability of the blood glucose level calculated by the blood glucose level calculation unit 52. This makes it possible to calculate a blood glucose level with estimated reliability. Therefore, the blood glucose level measuring device 1 allows the blood glucose level of the living body 6 to be measured accurately.

[0062] The similarity estimation unit 53 estimates the waveform similarity based on a normalized oxygenated hemoglobin waveform P11 obtained by dividing the oxygenated hemoglobin waveform P1 by the peak value of the oxygenated hemoglobin waveform P1 and a normalized deoxygenated hemoglobin waveform P21 obtained by dividing the deoxygenated hemoglobin waveform P2 by the peak value of the deoxygenated hemoglobin waveform P2, thereby enabling accurate estimation of the waveform similarity.

[0063] The similarity estimation unit 53 estimates that the waveform similarity decreases as the standard deviation σ calculated based on the above formula (8) increases, thereby enabling the waveform similarity to be estimated with high accuracy.

[0064] The similarity estimation unit 53 estimates that the waveform similarity is greater as the first relative quality index R1 calculated based on the above formulas (9) and (10) is closer to 1. This allows the waveform similarity to be estimated with high accuracy.

[0065] If the waveform similarity is smaller than the threshold value, the notification unit 55 issues a remeasurement notification, thereby urging the person measuring the blood glucose level to measure again.

[0066] When the waveform similarity calculated based on the detection results of the first measurement light L1 and the second measurement light L2 is smaller than the threshold, the temporal phase difference calculator 51 calculates the temporal phase difference Δθ based on the detection results of either the first measurement light L1 or the second measurement light L2 and the third measurement light L3. The third wavelength of the third measurement light L3 is longer than the first wavelength of the first measurement light L1 and shorter than the second wavelength of the second measurement light L2. This ensures both the accuracy of spectroscopic measurement and the waveform similarity, allowing the blood glucose level to be measured accurately.

[0067] According to the blood glucose level measuring method of this embodiment, like the blood glucose level measuring device 1, it is possible to measure the blood glucose level of the living body 6 with high accuracy.

[0068] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above-described embodiment.

[0069] 15 , the similarity estimation unit 53 may estimate the waveform similarity using a method similar to that of the embodiment, based on the region from bottom point B1 to peak point S1 of the oxygenated hemoglobin normalized waveform P11 and the region from bottom point B2 to peak point S2 of the deoxygenated hemoglobin normalized waveform P21. This allows the waveform similarity to be estimated efficiently. The similarity estimation unit 53 may estimate the waveform similarity based on at least a portion of the oxygenated hemoglobin normalized waveform P11 and at least a portion of the deoxygenated hemoglobin normalized waveform P21.

[0070] The similarity estimation unit 53 may estimate that the waveform similarity is greater as the standard inner product calculated based on the following formula (11) approaches 1. This allows the waveform similarity to be estimated with high accuracy.

[0071] P: standard inner product n: number of samples (an integer of 2 or more) pk: value of the oxygenated hemoglobin normalized waveform P11 at the kth time qk: value of the deoxygenated hemoglobin normalized waveform P21 at the kth time

[0072] The similarity estimation unit 53 may estimate that the waveform similarity decreases as the absolute mean error calculated based on the following formula (12) increases. This allows the waveform similarity to be estimated with high accuracy.

[0073] M: Absolute mean error n: Number of samples (an integer of 2 or more) pk: Value of the normalized oxygenated hemoglobin waveform P11 at the kth time qk: Value of the normalized deoxygenated hemoglobin waveform P21 at the kth time

[0074] Assuming that the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21 are each a sine wave, the theoretical limit value Mt of the absolute mean error M is the absolute value of Δθ divided by π / 2. The similarity estimation unit 53 may estimate that the waveform similarity increases as the reciprocal of the absolute mean error M approaches the reciprocal of the theoretical limit value Mt. In other words, the similarity estimation unit 53 may estimate that the waveform similarity increases as the second relative quality index calculated based on the following equations (13) and (14) approaches 1. This allows the waveform similarity to be estimated with high accuracy.

[0075] R2: Second relative quality index M: Absolute mean error Mt: Theoretical limit of absolute mean error Δθ: Temporal phase difference

[0076] The similarity estimation unit 53 may estimate the waveform similarity based on the image recognition results of the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21. This allows for accurate estimation of the waveform similarity. Specifically, the similarity estimation unit 53 performs a resizing process on each of the images of the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21, and then performs a binarization process on them. The similarity estimation unit 53 superimposes the binarized oxygenated hemoglobin normalized waveform P11 and the binarized deoxygenated hemoglobin normalized waveform P21 on the same coordinate system. The similarity estimation unit 53 calculates the sum (total number of non-overlapping pixels) of the number of pixels of the oxygenated hemoglobin normalized waveform P11 that do not overlap with pixels of the deoxygenated hemoglobin normalized waveform P21 and the number of pixels of the deoxygenated hemoglobin normalized waveform P21 that do not overlap with pixels of the oxygenated hemoglobin normalized waveform P11. The similarity estimation unit 53 calculates a value (non-overlapping pixel ratio) by dividing the total number of non-overlapping pixels by the total number of pixels in the coordinate system. The similarity estimation unit 53 calculates a value by subtracting the non-overlapping pixel ratio from 1 as a quality index. The similarity estimation unit 53 estimates that the waveform similarity is greater as the quality index approaches 1. Note that the similarity estimation unit 53 may set the temporal phase difference Δθ to zero when superimposing the oxygenated hemoglobin normalized waveform P11 and the deoxygenated hemoglobin normalized waveform P21 in the coordinate system. The similarity estimation unit 53 may calculate the quality index using the formula q = 1 / exp(kp), where q is the quality index, p is the non-overlapping pixel ratio, and k is a positive coefficient (any positive number). The closer the non-overlapping pixel ratio p is to zero, the greater the rate of increase of the quality index q. Even in this case, the similarity estimation unit 53 estimates that the closer the quality index q is to 1, the greater the waveform similarity.

[0077] In the embodiment, the ECU 5 is provided in the main body 2, but the ECU 5 does not have to be provided in the main body 2. The ECU 5 may be provided in, for example, a server that can communicate with the main body 2. In this case, the main body 2, the light output unit 3, the light detection unit 4, and the ECU 5 are each component of the blood glucose measurement system.

[0078] The blood glucose level calculation unit 52 may calculate changes in blood glucose levels over time. If a low-reliable blood glucose level is present among the blood glucose levels at multiple times, the blood glucose level calculation unit 52 may discard the low-reliable blood glucose level. In this case, the blood glucose level calculation unit 52 may use blood glucose levels before and after the low-reliable blood glucose level to complement the blood glucose level at the time corresponding to the low-reliable blood glucose level. The blood glucose level calculation unit 52 may, for example, calculate the average of blood glucose levels before and after the low-reliable blood glucose level as the blood glucose level at the time corresponding to the low-reliable blood glucose level.

[0079] The blood glucose level calculation unit 52 may calculate the blood glucose level multiple times and calculate the average value of the multiple blood glucose levels. If the reliability of each blood glucose level is relatively low, the blood glucose level calculation unit 52 may increase the number of times the blood glucose level is calculated. This ensures the accuracy of blood glucose level measurement even if the multiple blood glucose levels include a blood glucose level with a relatively low reliability.

[0080] 1...blood glucose level measuring device, 3...light output unit, 4...light detection unit, 6...living body, 51...temporal phase difference calculation unit, 52...blood glucose level calculation unit, 53...similarity estimation unit, 54...reliability estimation unit, 55...notification unit, L...measuring light, L1...first measuring light, L2...second measuring light, L3...third measuring light, P1...oxygenated hemoglobin waveform, P2...deoxygenated hemoglobin waveform, P11...oxygenated hemoglobin normalized waveform, P21...deoxygenated hemoglobin normalized waveform, Δθ...temporal phase difference.

Claims

1. A blood glucose level measuring device for measuring a blood glucose level of a living organism, comprising: a light output unit that outputs light to the living organism; a light detection unit that detects the light output by the light output unit and transmitted through the living organism; a temporal phase difference calculation unit that calculates a temporal phase difference between an oxygenated hemoglobin waveform related to the oxygenated hemoglobin concentration of the blood of the living organism and a deoxygenated hemoglobin waveform related to the deoxygenated hemoglobin concentration of the blood of the living organism based on the detection result of the light detection unit; a blood glucose level calculation unit that calculates the blood glucose level of the living organism based on the temporal phase difference calculated by the temporal phase difference calculation unit; a similarity estimation unit that estimates a waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform; and a reliability estimation unit that estimates a reliability of the blood glucose level calculated by the blood glucose level calculation unit, wherein the reliability estimation unit estimates that the reliability decreases as the waveform similarity decreases.

2. The blood glucose level measuring device of claim 1, wherein the similarity estimation unit estimates the waveform similarity based on an oxygenated hemoglobin normalized waveform obtained by dividing the oxygenated hemoglobin waveform by the peak value of the oxygenated hemoglobin waveform and a deoxygenated hemoglobin normalized waveform obtained by dividing the deoxygenated hemoglobin waveform by the peak value of the deoxygenated hemoglobin waveform.

3. The blood glucose measuring device according to claim 2, wherein the similarity estimation unit estimates that the waveform similarity is smaller as the standard deviation calculated based on the following formula (1) is larger: where σ is the standard deviation, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

4. The blood glucose measuring device according to claim 3, wherein the similarity estimation unit estimates that the waveform similarity is greater the closer the first relative quality index calculated based on the following equations (2) and (3) is to 1. where R1 is the first relative quality index, σ is the standard deviation, σt is the theoretical limit value of the standard deviation, and Δθ is the temporal phase difference.

5. The blood glucose measuring device according to claim 2, wherein the similarity estimation unit estimates that the waveform similarity is greater as the standard inner product calculated based on the following formula (4) approaches 1: where P is the standard inner product, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

6. The blood glucose measuring device according to claim 2, wherein the similarity estimation unit estimates that the waveform similarity is smaller as the absolute mean error calculated based on the following formula (5) is larger: where M is the absolute mean error, n is the number of samples (an integer of 2 or more), pk is the value of the normalized oxygenated hemoglobin waveform at the kth time, and qk is the value of the normalized deoxygenated hemoglobin waveform at the kth time.

7. The blood glucose measuring device according to claim 6, wherein the similarity estimation unit estimates that the waveform similarity is greater the closer the second relative quality index calculated based on the following equations (6) and (7) is to 1. where R2 is the second relative quality index, M is the absolute mean error, Mt is the theoretical limit value of the absolute mean error, and Δθ is the temporal phase difference.

8. The blood glucose measuring device according to claim 2, wherein the similarity estimation unit estimates the waveform similarity based on the image recognition results of the oxygenated hemoglobin normalized waveform and the deoxygenated hemoglobin normalized waveform.

9. The blood glucose measuring device of claim 2, wherein the similarity estimation unit estimates the waveform similarity based on the region from the bottom point to the peak point of the oxygenated hemoglobin normalized waveform and the region from the bottom point to the peak point of the deoxygenated hemoglobin normalized waveform.

10. The blood glucose measuring device according to claim 1, further comprising a notification unit that issues a remeasurement notification when the waveform similarity is smaller than a predetermined threshold value.

11. The blood glucose level measuring device of claim 1, wherein the light detection unit detects first light having a first wavelength, second light having a second wavelength, and third light having a third wavelength as the light that has passed through the living body; the temporal phase difference calculation unit calculates the temporal phase difference based on the detection results of either the first light or the second light, and the third light, when the waveform similarity calculated based on the detection results of the first light and the second light is smaller than a predetermined threshold; and the third wavelength is greater than the first wavelength and less than the second wavelength.

12. A blood glucose level measuring method for measuring a blood glucose level of a living organism, comprising: a temporal phase difference calculation step of calculating a temporal phase difference between an oxygenated hemoglobin waveform relating to the oxygenated hemoglobin concentration in the blood of the living organism and a deoxygenated hemoglobin waveform relating to the deoxygenated hemoglobin concentration in the blood of the living organism based on the detection result of light transmitted through the living organism; a blood glucose level calculation step of calculating the blood glucose level of the living organism based on the temporal phase difference calculated in the temporal phase difference calculation step; a similarity estimation step of estimating waveform similarity between the oxygenated hemoglobin waveform and the deoxygenated hemoglobin waveform; and a reliability estimation step of estimating reliability of the blood glucose level calculated in the blood glucose level calculation step, wherein in the reliability estimation step, it is estimated that the reliability is lower as the waveform similarity is lower.

13. The blood glucose measurement method according to claim 12, further comprising: a light output step of outputting the light to the living body; and a light detection step of detecting the light output in the light output step and transmitted through the living body.

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